Four-component alumina base catalyst and its preparation



Patented Aug. 15, 1950 FOUR-COMPONENT ALUMINA BASE CATA- LYST AND ITS PREPARATION Robert L. Parker, Jr., Huntington Park, and Hal C. Hufiman, Long Beach, CaliiL, aslignors to Union Oil Company of California, Los Angeles, Calii., a corporation of California No Drawing.

Original application December 21,

1943, Serial No. 515,122. Divided and this application July 8, 1946, Serial N0. 682,126

9 Claims. 1

This invention relates to the catalytic conversion of hydrocarbons and. particularly to the dehydrogenation of normally gaseous hydrocarbons in the presence of a novel catalyst.

It is known that when hydrocarbons are subjected to elevated temperatures in the presence of catalysts, they may be converted" or changed in form. Well known conversion processes for example include cracking, reforming, and the like, as well as dehydrogenation and the like. The type of conversion which occurs depends not only on the reaction conditions, but on the type of catalyst employed. Some catalysts appear to aflect predominantly the carbon to carbon bonds of the hydrocarbon, while others affect predominantly the carbon to hydrogen bonds. It is clear that a catalyst of the former type should preferentially promote cracking reactions, while a catalyst of the latter type should preferentially promote dehydrogenation reactions, and this has been observed to be true in a general way. Silica, for example, appears to affect carbon to carbon bonds to a much greater extent than does alumina, and consequently in making dehydrogenation catalysts, although alumina is frequently employed in substantial proportions as a carrier, silica is generally avoided.

This is a division of application Ser. No. 515,122, filed December 21, 1943, which issued August 19, 1947, as Patent No. 2,426,118.

It has now been discovered that the presence of a small proportion of silica in dehydrogenation catalysts, contrary to the indications of the prior art, is highly desirable, particularly with regard to increasing the stability of the catalyst toward heat, and preserving its activity over a longer useful life. This desirable effect of silica is particularly evident in the case of dehydrogenation of normally gaseous hydrocarbons, in which process the optimum proportion of silica in the catalyst is about 1% by weight.

It is an object of this invention therefore, to provide an eflicient. dehydrogenation process, whereby acyclic hydrocarbons having 2 to 5 carbon atoms may be catalyticallytreated to increase their degree of unsaturationj for example, butanes may be converted to butenes and butadiene, butenes may be convertedto butadiene, propane may be converted to propene, and pentanes may be converted to pentenes, isoprene, etc. further object to provide a novel and exceptionally useful catalyst for this process. Other objects will become apparent.

We have discovered that by incorporating a small amount of silica such as about 1%, in a Itisa catalyst consisting predominantly of an alumina gel carrier impregnated with minor proportions of chromia and beryllia, the dehydrogenating activity of the catalyst is enhanced, its heat stability is increased, and its eflective life is lengthened. The resulting catalyst is particularly effective for the dehydrogenationoi' butanes to butenes and butenes to butadiene. This type of dehydrogenation is of great importance at the present time because of the extensive use of butenes in alkylation processes for the production of aviation gasoline, and the use of both butenes and butadiene in the preparation of synthetic rubber and plastics.

As a specific example of our invention, a carrier consisting of an alumina gel containing 0.9% silica was prepared by precipitation ofthe hydrous oxides from aqueous solutions of soluble salts of aluminum and silicon, and this carrier was ignited in air at about 500 C. for about 2 hours to convert it into a hard highly adsorptive gel. This product, screened to 8 to 20 mesh size, was then impregnated with solutions of beryllium and chromium salts as follows: to 900 grams of the ignited carrier was added 379 grams of beryllium nitrate Be(N0a)2.3HzO dissolved in 800 ml. of distilled water. dryness with constant agitation, and the resulting material was dried for 16 hours at about 250 C. followed by a 2 hour ignition at 500 C. To this beryllia-impregnated product was added a solution of 84 grams of ammonium dichromate (NI-I4) zCrzOv dissolved in 800 ml. of distilled water, and this mixture was heated to dryness with agitation, dried and ignited as above, to obtain a finished catalyst containing about by weight 5 liters per hour through 5 ml. of the above catalyst in a reaction chamber at a temperature of about 565 C. (1050 F.) and substantially atmospheric pressure. This feed rate corresponds to a space velocity (volumes of feed gas, measured at 0 C. and 760 mm. pressure, per volume of catalyst per hour) of 912. Under these conditions, the average conversion of butane to butenes over a 2-hour reaction cycle was 34.4% (mol per cent) which is not far from the maximum theoretically possible (equilibrium) conversion at this temperature. The catalyst was then regenerated by substituting a smaller flow of air for the nbutane flow for a period of about 6 hours atabout The mixture was heated to the same tempera ure. Butane was then substituted for the air flow for another 2-hour cycle similar to the first cycle, and substantially the same conversion was obtained.

The heat stability, life, strength, and other characteristics of the above catalyst are all remarkably good, as brought out in the following paragraphs.

A heat stability test for catalysts has been developed which will be referred to as the 850 C. calcination test. In this test a sample of catalyst is subjected to a temperature of 850 C. in air for a period of 6 hours. At the end of this time its physical characteristics and catalytic activity are again determined, and any changes brought about by the calcination are noted. Usually, it is found that catalysts supported on alumina lose their hardness, become soft and powdery, and lose most of their catalytic activity. This is true to a limited extent even of the above catalyst when the silica is omitted from its composition. With the silica incorporated however, the above catalyst upon calcination at 850 C. retained substantially entirely its original form and mechanical strength, and gave a 24% conversion of butanes to butenes when tested as above. The 850 C. calcination test has been found to be a fairly reliable index of the behavior of dehydrogenation catalysts over extended periods of usage; i. e., a good retention of strength and. activity upon calcination at 850 C. generally indicates that the catalyst will also have a good retention of strength and activity in use over an extended period of time. The results of the above test indicate that this catalyst will preserve its strength and excellent activity through many hundreds of cycles of use and regeneration as described above.

The explanation for the remarkable effect of the silica on the catalyst as described above is not known. It is onlyknown that the silicapromoted catalysts of the type described above have tremendous surface'area, larger than that Of any other dehydrogenation catalysts of similar type; and it also appears that the presence of the silica with the aluminaprevents or at least retards the conversion of the alumina to an inactive form.

The above catalyst is also very effective for the production of butadiene, either from butanes or butenes. For this dehydrogenation operation slightly higher temperatures are preferable, in the neighborhood of 600 C., and the effective pressure should be lower, in the neighborhood of 100 to 500 mm. of mercury. These low effective pressures may be attained either by operating under vacuum at these total pressures, or by employing total pressures as high as 2 or even atmospheres, and having a diluent or inert gas such as nitrogen, methane and the like, present in such proportions as to lower the effective pressure (1. e., the partial pressure of the hydrocarbons being converted) to a value within the desired range. When butane is being dehydrogenated to butadiene, longer contact times, i. e., lower space velocities, such as about 300 or less may be used, while in the dehydrogenation of butenes, higher space velocities, such as 3000 or more may be used. In general the most suitable temperatures for butane and butene dehydrogenation are between about 550 C. and 650 C., with higher space velocities being employed at the higher temperatures.

Other "normally gaseous acyclic hydrocarbons having 2 to 5 carbon atoms may also be dehydro- 4 genated preferably under the conditions given above, although somewhat higher temperatures are desirable for the dehydrogenation of ethane and propane, while somewhat lower temperatures are desirable for the dehydrogenation of the pentanes.

For the above dehydrogenation process, the preferred catalysts are of the type indicated above, 1. e., they should consist of a gel W alumina carrier containing about 1% of silica, impregnated with solutions of chromium and berylliumandignitedsoastoobtainaflnished catalyst containing about 1% to 15% of ch'romia and about 1% to 15% of beryllia, by weight. For the purpom of this invention, beryllia concentrations of 1% to 5% are preferred.

Although sillcaconcentrations of about 1% are preferred, the silica has a pronounced beneficial effect even when present in 0.5% or lower concentrations, and up to about 5%, and even in some instances as high as 15%.

The beneficial effects of small amounts of silica are not entirely limited to the above catalysts nor to the above dehydrogenation process, however. It has been found, for example, that catalysts of the above type are excellent for all sorts of hydrocarbon conversion processes such as cracking of gas oils and the like; isomerization of olefins, and naphthenes; reforming. aromatization and hydroforming of gasolines and naphthas; and like processes which are carried out at temperatures between about 400 C. and 900 C. in the presence or absence of hydrogen. In hydroforming operations for example, which are preferably carried out on liquid hydrocarbons such as petroleum naphthas, at temperatures between about 400 C. and 600 C. and pressures of 10 or more atmospheres, in the presence of about 2000 to 10,000 cubic feet of hydrogen per barrel of feed, the above catalysts are excellent, especially when the silica content is about 5%. or lies between about 1% and 10%. For catalytic cracking of gas oils, which is generally carried out at temperatures between 450 C. and 550 0.. similar catalysts containing up to about 15% silica are preferred. All of the above processes are included in the term catalytic dehydrogenation of hydrocarbons as used in the claims.

The alumina in the above catalysts is preferably the gel type, and may be prepared by precipitation with ammonia of an aluminum chloride, nitrate, or sulfate solution, with thorough washing of the precipitate to remove soluble salts, or by any other suitable method for obtaining a gelatinous alumina carrier. The silica is preferably coprecipitated with the alumina from a silicon tetrachloride solution or other solution, but may be separately precipitated and adsorbed on the hydrous gelatinous alumina. The carrier of alumina-silica is dried and ignited at about 500 C. to 600 C. to "activate" it and increase its adsorptive power. It may be ground and pelleted, or extruded, or merely broken into granules of suitable size, either before or after igniting. Commercial alumina may also be used, especially if it is the gel type. Crystalline, corundum, or alpha alumina, however, is not effective in our catalysts.

In incorporating the chromium and beryllium into the above carriers, the impregnation procedure as described above or merely dipping the ignited carrier in the solution of the chromium or beryllium salt are preferred methods, but the chromium or beryllium hydroxides may also be coprecipitated with the alumina and silica, as by addition of ammonia to the solutions the nitrates or chlorides. I1 coprecipitated, the product is dried, pelleted, etc. as described for the carrier.

It has been found that catalysts in which the other metals of group VI B such as tungsten, uranium, and particularly molybdenum, are substituted for part or all of the chromium in the above catalysts, are also beneficially efiected by the presence of small amounts of silica. In fact the presence of about 0.5 to 15%, preferably about 1% to 5% of silica incorporated as above, improves any catalyst consisting of an active alumina (this term does not include the crystalline, corundum, or alpha aluminas mentioned above but does include gel aluminas) in combination with an oxide of metals of group VI B as described above. The oxides of these active metals may be mixed, i. e., deposited on the silica-alumina in the form of mixtures of oxides or of compounds including 2 or more metals, such as cobalt molybdate, cobalt thiomolybdate,

copper vanadate, nickel chromite, and the like.

It is preferable that such catalysts contain a minor proportion of beryllia also, such as about 1% to 15% as indicated above. The beryllia does not appear to have a catalytic effect by itself, such as is the'case with the above active metal oxides, but it appears to promote and increase the catalytic eflect of the active metal oxides. This effect may or may not be analogous to the effect of the silica on the active alumina.

It has also been found that the desirable ef- !ects of silica on the above catalysts for hydrocarbon conversion, are also imparted by zirconia, and even by titania, although the silica is preferred. Silicon, titanium, and zirconium are all elements of group IV of the periodic system. The zirconia and titania may be employed in about the same amounts as the silica, i. e. about 0.5% to 15%, and are also preferably incorporated in the alumina by coprecipltation.

It is within the scope of this invention therefore to provide a process for the conversion of hydrocarbons and a catalyst therefore which comprises an active alumina containing small amounts of silica and compound of an active metal, and preferably also a compound of beryllium.

Modifications 01' this invention which would occur to one skilled in the art are to be considered within the scope oi! the invention as delined in the following claims.

We claim:

1. A catalyst which consists essentially of four components, namely an active alumina gel carrier containing about 0.5% to 15% of an oxide of an element of group IV selected from the class 6 consisting of silicon, titanium and zirconium precipitated thereon, about 1% to 15% of beryllia, and a minor proportion between about 1% and about 15% of a catalytic agent selected from the class consisting of the oxides of the metals of group VI B.

2. A catalyst according to claim 1 in which the group IV element is silicon.

3. A catalyst according to claim 1 in which the metal of group VI B is chromium.

4. A catalyst according, to claim 1 in which the metal of group VI B is molybdenum.

5. A catalyst which consists essentially of four components, namely an active alumina gel carrier containing about 0.5% to 15% of silica precipitated thereon, about 1% to 15% of beryllia, and a minor proportion between about 1% and about 15% of a catalytic agent comprising chromium oxide.

6. A catalyst according to claim 5 in which rier containing about 0.5% to 15% of silica precipitated thereon, about 1% to 15% of beryllia, and a minor proportion between about 1% and about 15% of a catalytic agent comprising molybdenum oxide.

8.- A catalyst according to claim. '7 in which the catalytic agent is cobalt molybdate.

9. A method of preparing a catalyst which comprises coprecipitating hydrous alumina with about 0.5% to 15% of a hydrous oxide of an element of group IV selected from the class consisting of silicon, titanium and zirconium, drying and igniting the precipitate, and impregnating thereon about 1% to 15% of beryllia, and a minor proportion between about 1% and about 15% of an oxide of a metal of group VI B and mixtures thereof.

ROBERT L. PARKER, Ja. HAL C. HUFFMAN.

REFERENCES CITED The following references are oi record in the file of this patent:

{3 UNITED STATES PATENTS Number Name Date 2,209,908 Weiss July 30, 1940 2,215,305 Voorhies Sept. 1'7, 1940 2,243,404 Voorhies May 27, 1941 2,283,172 Bates May 19, 1942 2,325,033 Byrns July 27, 1943 2,394,516 Goshorn Feb. 5, 1946 2,395,836 Bates Mar. 5, 1946 2,411,829 Huiiman Nov. 26, 1946 2,418,270 Maruszak Apr. 1, 1947 2,426,118 Parker et a1. Aug. 19, 1947 

1. A CATALYST WHICH CONSISTS ESSENTIALLY OF FOUR COMPONENTS, NAMELY AN ACTIVE ALUMINA GEL CARRIER CONTAINING AVOUT 0.5% TO 15% OF AN OXIDE OF AN ELEMENT OF GROUP IV SELECTED FROM THE CLASS CONSISTING OF SILICON, TITANIUM AND ZIRCONIUM PRECIPITATED THEREON, ABOUT 1% TO 15% OF BERYLLIA, AND A MINOR PROPORTION BETWEEN ABOUT 1% AND ABOUT 15% OF A CATALYSTIC AGENT SELECTED FROM THE CLASS CONSISTING OF THE OXIDES OF THE METALS OF GROUP VI B. 